U.S. patent number 4,016,722 [Application Number 05/573,984] was granted by the patent office on 1977-04-12 for safety blow-out protection for fluid actuators.
This patent grant is currently assigned to Gould Inc.. Invention is credited to Otto C. Niederer, Sr..
United States Patent |
4,016,722 |
Niederer, Sr. |
April 12, 1977 |
**Please see images for:
( Certificate of Correction ) ** |
Safety blow-out protection for fluid actuators
Abstract
Excessive pressure is relieved in a fluid actuator by controlled
destruction of an internal extensible diaphragm without damage to
the exterior structural integrity of the actuator. Upon occurrence
of such abnormal excessive pressure in the actuator pressure
chamber, the diaphragm, which is otherwise substantially supported,
is permitted to deform at a known location until fracturing thereof
occurs to release fluid from the pressure chamber. In one form the
invention comprises an opening in the actuator guide cap and in
other forms comprises openings in the actuator piston or an
enlargement in part of the guide cap.
Inventors: |
Niederer, Sr.; Otto C.
(Madison, OH) |
Assignee: |
Gould Inc. (Chicago,
IL)
|
Family
ID: |
24294204 |
Appl.
No.: |
05/573,984 |
Filed: |
May 2, 1975 |
Current U.S.
Class: |
60/531; 60/530;
60/527 |
Current CPC
Class: |
F15B
15/10 (20130101); F15B 21/06 (20130101) |
Current International
Class: |
F15B
15/10 (20060101); F15B 15/00 (20060101); F15B
21/06 (20060101); F15B 21/00 (20060101); F03G
007/06 () |
Field of
Search: |
;60/516,527-531
;337/114,306,416 ;73/368.3 ;92/98D ;91/400,401 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ostrager; Allen M.
Attorney, Agent or Firm: Donnelly, Maky, Renner &
Otto
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A fluid actuator device, comprising a body, an extensible means
in sealed engagement with said body for forming a variable volume
pressure chamber, said extensible means being movable with respect
to said body to effect changes in the volume of said pressure
chamber and thus to convert normal pressure variations in said
pressure chamber to mechanical energy, said extensible means
comprising a diaphragm, means for controllably relieving pressure
in said pressure chamber when an abnormal pressure level occurs
therein in excess of a predetermined level, said means for
controllably relieving comprising means for facilitating controlled
fracturing of said diaphragm.
2. A fluid actuator device as set forth in claim 1, further
comprising a thermally responsive liquid substantially filling said
pressure chamber when said fluid actuator device is in de-energized
condition, and means for applying heat to said liquid effecting
vaporization and expansion of at least a part of the same to cause
a corresponding increase in fluid pressure in said pressure
chamber.
3. A fluid actuator device as set forth in claim 1, further
comprising means for supporting a portion of said diaphragm on its
side remote from said pressure chamber.
4. A fluid actuator device as set forth in claim 3, said means for
supporting comprising guide cap means for generally confining said
diaphragm for linear movement thereof.
5. A fluid actuator device, comprising a body, an extensible means
in sealed engagement with said body for forming a variable volume
pressure chamber, said extensible means comprising a diaphragm
movable with respect to said body to effect changes in the volume
of said pressure chamber and thus to convert normal pressure
variations in said pressure chamber to mechanical energy, means for
supporting a portion of said diaphragm on its side remote from said
pressure chamber, said means for supporting comprising guide cap
means for limiting extension of said diaphragm, and means for
relieving pressure in said pressure chamber when an abnormal
pressure level occurs therein in excess of a predetermined level,
said means for relieving comprising means for facilitating
controlled fracturing of said diaphragm and said means for
facilitating comprising an opening in an otherwise diaphragm
supportive portion of said guide cap means, said diaphragm being
unsupported at said opening.
6. A fluid actuator device as set forth in claim 4, said diaphragm
having a cap portion projecting into said pressure chamber and an
annular fold along which said diaphragm may roll for varying said
projection to effect a corresponding change in the volume of said
pressure chamber, said means for supporting further comprising a
piston in supportive engagement with said diaphragm cap
portion.
7. A fluid actuator device as set forth in claim 6, said diaphragm
having an outer generally cylindrical leg substantially completely
supported by said guide cap means, said piston substantially
completely supporting said diaphragm cap portion, said annular fold
normally being unsupported, and said opening being located in said
guide cap means to permit part of said diaphragm at said annular
fold to extend therethrough upon occurrence of such abnormal
pressure in said pressure chamber.
8. A fluid actuator device as set forth in claim 7, said guide cap
means having a step portion that limits maximum extension of said
diaphragm annular fold, and said opening being located at least
partially in said step portion.
9. A fluid actuator device, comprising a body, an extensible means
in sealed engagement with said body for forming a variable volume
pressure chamber, said extensible means comprising a diaphragm
movable with respect to said body to effect changes in the volume
of said pressure chamber and thus to convert normal pressure
variations in said pressure chamber to mechanical energy, means for
supporting a portion of said diaphragm on its side remote from said
pressure chamber, said means for supporting comprising guide cap
means for generally confining said diaphragm for linear movement
thereof, and said means for supporting further comprising a piston
in supportive engagement with part of said diaphragm, and means for
relieving pressure in said pressure chamber when an abnormal
pressure level occurs therein in excess of a predetermined level,
said means for relieving comprising means for facilitating
controlled fracturing of said diaphragm, and said means for
facilitating comprising an opening in an otherwise normally
diaphragm supportive portion of said piston, said diaphragm being
unsupported at said opening and capable of fracturing and releasing
fluid through the same upon occurrence of such abnormal pressure in
said pressure chamber.
10. A fluid actuator device as set forth in claim 9, further
comprising piston rod means having a portion extending through an
opening in said guide cap means for transmitting mechanical
movements of said piston to a location externally of said guide cap
means, and a clearance between said piston rod means and said guide
cap means opening to provide an exit flow path for fluid released
by such a fractured diaphragm.
11. A fluid actuator device as set forth in claim 9, said piston
including a skirt portion having an exterior profile generally
corresponding to the interior profile of said guide cap means,
whereby said skirt portion and guide cap means cooperate to provide
guidance for said piston for linear movement thereof in said guide
cap means, and said opening being located in said piston skirt
portion.
12. A fluid actuator device as set forth in claim 11, said
diaphragm having a cap portion projecting into said pressure
chamber and an annular fold along which said diaphragm may roll for
varying said projection to effect a corresponding change in the
volume of said pressure chamber, said piston being in supportive
engagement with said diaphragm cap portion, and said piston skirt
portion being able to provide a supportive function to said
diaphragm annular fold.
13. A fluid actuator device as set forth in claim 9, said diaphragm
having a cap portion projecting into said pressure chamber and an
annular fold along which the diaphragm may roll for varying said
projection to effect a corresponding change in the volume of said
pressure chamber, said piston being in supportive engagement with
said diaphragm cap portion, said diaphragm having an outer
substantially cylindrical leg substantially completely supported by
said guide cap means, said piston having a flat end and a generally
cylindrically-shaped surface substantially completely supporting
said diaphragm cap portion, and said opening in said piston
comprising a generally longitudinal slot in said piston generally
cylindrically-shaped surface.
14. A fluid actuator device as set forth in claim 13, said piston
having a cylindrical opening in which a return spring is
positioned, said return spring being also in engagement with a
portion of said guide cap means to apply a force to said piston
normally urging said projection into said pressure chamber when the
fluid actuator device is de-energized, said longitudinal slot
opening into said cylindrical opening for release of fluid
therethrough.
15. A fluid actuator device as set forth in claim 14, wherein the
longitudinal sidewalls defining said longitudinal slot are
substantially parallel.
16. A fluid actuator device as set forth in claim 14, wherein the
longitudinal sidewall defining said longitudinal slot are flared at
an acute angle with respect to each other.
17. A fluid actuator device, comprising a body, an extensible means
in sealed engagement with said body for forming a variable volume
pressure chamber, said extensible means comprising a diaphragm
movable with respect to said body to effect changes in the volume
of said pressure chamber and thus to convert normal pressure
variations in said pressure chamber to mechanical energy, means for
supporting a portion of said diaphragm on its side remote from said
pressure chamber, said means for supporting comprising guide cap
means for limiting extension of said diaphragm and guiding the
latter for generally linear movement and a piston in supportive
engagement with part of said diaphragm, said piston and guide cap
means having cooperable portions substantially to limit the maximum
extension of said diaphragm, and means for relieving pressure in
said pressure chamber when an abnormal pressure level occurs
therein in excess of a predetermined level, said means for
relieving comprising means for facilitating controlled fracturing
of said diaphragm, and said means for facilitating comprising an
enlargement of said cooperable portion of said guide cap means to
permit further extension of part of said diaphragm into the same
upon occurrence of such abnormal pressure in said pressure
chamber.
18. A fluid actuator device as set forth in claim 17, said
diaphragm having a cap portion projecting into said pressure
chamber and an annular fold along which said diaphragm may roll for
varying said projection to effect a corresponding change in the
volume of said pressure chamber, said diaphragm having an external
cylindrical leg terminating in a fluid seal with said body, said
guide cap means including two substantially cylindrical portions
connected at a substantially annular step, the first and larger
diameter portion of said guide cap means being normally in
supportive engagement with said diaphragm cylindrical leg, said
piston being normally in supportive engagement with said diaphragm
cap portion and being movable into the second and smaller diameter
portion of said guide cap means, said piston having a generally
cylindrically-shaped surface which together with said step and
second guide cap means portion form the mentioned cooperable
portions and said enlargement comprising an extension of said first
larger diameter portion into the area of the second smaller
diameter portion of said guide cap means to permit extension
thereinto of a limited part of said diaphragm at its annular fold
for fracturing of that diaphragm part upon occurrence of such
abnormal pressure in said pressure chamber.
19. A fluid actuator device as set forth in claim 18, further
comprising piston rod means having a portion extending through an
opening in said guide cap means for transmitting mechanical
movements of said piston to a location externally of said guide cap
means, and a clearance between said piston rod means and said guide
cap means opening to provide an exit flow path for fluid released
by such a fractured diaphragm.
Description
BACKGROUND OF THE INVENTION
This invention is directed to a pressure relief arrangement for a
fluid actuator, and, more particularly, is directed to such a
pressure relief arrangement for a linear fluid actuator that
converts a thermal input to a mechanical output.
Electro-thermal actuators and other fluid actuator devices that
restrain a fluid pressure by means of a rolling diaphragm are
sometimes subject to pressures great enough to cause violent
disassociation of the parts constituting the actuator. In a thermal
actuator, such a high pressure might occur if the unit were heated
well beyond normal operating conditions, for example, by a fire
occurring in the building in which the actuator were located.
Moreover, in those electrothermal actuators normally energized for
short intervals, a prolonged energization of the same might effect
such an undesirable large pressure build up. Thus, abnormal
excessive pressure build up may be due to external ambient or
overload conditions of the actuator, excesssive energization input,
etc.
The present invention which provides relief of excessive pressures
in a fluid actuator device without violent disassociation of the
parts thereof, will be described in detail herein with reference to
an electro-thermal linear fluid actuator device or thermal
actuator, as shown, for example, in U.S. Pat. Nos. 3,609,635 and
3,805,528. Such a thermal actuator includes a main body or casing
and an extensible member, such as a diaphragm in sealed engagement
with the body to define a fluid chamber having a volume that is
variable according to the position of the extensible member with
respect to the body. By heating a thermally expansive working
medium in the chamber, the pressure therein is increased and tends
to urge the extensible member away from the body expanding the
chamber and performing mechanical work. It is to be understood,
however, that the principles of the invention may be applied to
other types of fluid actuator devices, especially linear fluid
actuator devices, such as those that operate in response to a
pneumatic or hydraulic fluid input to the chamber.
SUMMARY OF THE INVENTION
The present invention is directed to an arrangement for
facilitating perforation of the extensible member in a fluid
actuator device for controlled relief of excessive pressure in such
device. The extensible member may be, for example, a diaphragm
having a cap portion that projects into the fluid chamber defined
in the main body of the actuator and an annular fold along which
the diaphragm may roll with minimum resistance for enlargement and
reduction of the chamber volume, and the invention provides for
controlled rupturing or fracturing of the diaphragm to release
excessive pressure in the fluid chamber. Of course, other types of
extensible member may be used. In one embodiment the invention
takes the form of a hole in the normally supportive guide casing of
the actuator device, and in another embodiment the invention
includes an embossment on the guide casing. In still other
embodiments the invention takes the form of a slot or opening in a
piston member that usually abuts the extensible member on its side
opposite the fluid chamber.
The primary object of the present invention is to provide a means
for causing a controlled relief of excessive pressure in a fluid
actuator by effecting a rupturing or fracturing of the diaphragm or
other extensible member thereof before the pressure in the actuator
fluid chamber reaches a dangerous level. Therefore, as pressure
increases in the fluid chamber, the diaphragm, which is
substantially supported, will tend to stretch at an unsupported
part, for example, through a hole provided in the guide casing. As
the pressure continues to increase the diaphragm portion protruding
through the hole will rupture to release the pressure at a pressure
level well below that at which violent disassociation of the
actuator assembly might occur, yet at a pressure level well above
those pressures normally obtained during normal operation of the
actuator.
With the foregoing in mind, it is a principal object of the present
invention to provide a fluid actuator device improved in the noted
respects.
Another object of the invention is to relieve excessive pressure in
the fluid chamber of a fluid actuator device.
An additional object of the invention is to provide controlled
relief of excessive pressure in a fluid actuator device.
A further object of the invention is to provide controlled
perforation or rupturing of an extensible member in a fluid
actuator device.
Still another object of the invention is to provide controlled
relief of excessive pressure in a fluid actuator device without
disassociation of the parts thereof.
Still an additional object of the invention is to provide a safety
blow-out arrangement for controlled relief of excessive pressures
in a fluid actuator device, thus increasing the safe operation of
such device.
These and other objects and advantages of the present invention
will become apparent as the following description proceeds.
To the accomplishment of the foregoing and related ends, the
invention, then, comprises the features hereinafter fully described
in the specification and particularly pointed out in the claims,
the following description and the annexed drawings setting forth in
detail certain illustrative embodiments of the invention, these
being indicative, however, of but several of the various ways in
which the principles of the invention may be employed.
BRIEF DESCRIPTION OF THE DRAWINGS
In the annexed drawings:
FIG. 1 is a section view of a de-energized thermal actuator having
a pressure relief hole in the guide casing;
FIG. 1A is an external isometric view of the thermal actuator of
FIG. 1;
FIG. 2 is a section view of the thermal actuator of FIG. 1 now in
the energized condition;
FIG. 3 is a section view of a de-energized thermal actuator
including a piston with a slotted supportive skirt;
FIG. 3A is an isometric view of the piston used in the thermal
actuator of FIG. 3;
FIG. 4 is a section view of a de-energized thermal actuator having
a pressure relief embossment in the guide casing;
FIG.4A is an external isometric view of the thermal actuator of
FIG. 4;
FIG. 5 is a section view of a de-energized thermal actuator
including a piston having a longitudinal slot for controlled
pressure relief; and
FIGS. 5A and 5B are isometric views of two different types of
pistons having longitudinal slots for use in the thermal actuator
of FIG. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now more particularly to the drawings, wherein like
reference numerals designate like parts in the several figures, and
initially to FIGS. 1, 1A and 2, a thermal actuator is generally
indicated at 1. As it appears externally in FIG. 1A, the thermal
actuator 1 includes a main body or casing 2, to which a stepped
guide cap or casing 3 is secured at a flange connection 4. A piston
rod or actuator rod 5 protrudes partially through an opening 6 in
the front end wall 7 of the guide cap 3, when the thermal actuator
is de-energized, and fully from that opening when the thermal
actuator is energized in the manner shown, for example, in FIG. 2.
A safety blow-out or pressure relief opening 8 is formed in the
guide cap 3, preferably proximate or at the annular step 9 thereof.
During normal operation of the thermal actuator 1, the pressure
relief opening 8 will have little or no effect; however, during
abnormal external and/or operating conditions of the thermal
actuator 1, which conditions would cause fluid pressure therein to
exceed the normally expected pressures, such excessive fluid
pressure will be relieved through the pressure relief opening 8
well before the fluid pressure would reach a dangerous level.
As shown in greater detail in FIGS. 1 and 2, an extensible
diaphragm member 10 is secured within and to the main body 2 at a
fluid tight seal 11 defined by an annular rim 12 of the diaphragm
which is captured by a crimped flange 13 of the body. A variable
volume fluid pressure chamber 14 is thus formed by the body 2 and
diaphragm 10, and a quantity of thermally expansible and
contractible material 15 is contained therein. An electric heater
16 in the fluid chamber 14 may be fed with electric power from an
external supply, not shown, via electrical leads 17 that pass
through electrically non-conductive seals 18 in the main body 2;
the heat generated by the heater 16 expands the material 15
increasing fluid pressure in the pressure chamber 14 and the force
on the diaphragm 10 tending to cause expansion of the chamber.
The extensible diaphragm member 10 is preferably in the form of a
cylindrical-shape diaphragm which is inverted or reverse-folded to
form a cap 19 defined by a relatively flat circular end 20 and a
cylindrical leg 21, and the cap portion joins a further cylindrical
leg portion 22 at an annular fold 23. The diaphragm rim 12
terminates the further cylindrical leg portion 22 and the cap
portion 19 forms a variable projection into the chamber 14, the
projection length increasing and decreasing with respective
increases and decreases in the chamber pressure.
The diaphragm material may be of the unreinforced or reinforced
type and may be formed of various types of natural and/or synthetic
materials, depending on the desired strength, resiliency, fluid
permeability, temperature dependency and the like parameters.
Moreover, it is, of course, to be understood that other types of
extensible members may be used, such as, for example, stretching
type diaphragms, bellows type devices, etc., the principal
operation criteria for selection of the extensible member being its
ability to provide for enlargement and reduction in the size of the
fluid chamber 14 as pressure in the latter is varied in order to
convert such pressure changes to a mechanical output in terms of
force and/or an output stroke over a distance.
The thermally expansible and contractible working fluid 15 is
selected to provide preferably a quick response when heated to
effect an increase in the pressure within the fluid chamber 14, and
it has been found that one satisfactory working fluid is a
halogenated hydrocarbon containing a fluorine atom, which fluid is
normally sold under the trademark "FREON". Such a working fluid
would normally be in a liquid phase at ambient temperatures and
will vaporize at about 200.degree. F.; and in the liquid phase such
fluids are relatively inertand dielectric. Another type of working
fluid suitable for use in the thermal actuator 1 is known as a
fluoro-inert liquid and is sold under the trademark "FC" by the 3-M
Company; one particular advantage to the FC fluids is their
capability of mixture of two or more such fluids to adjust the
boiling point thereof, and another advantage is their relatively
low permeability through diaphragms made of elastomeric materials
relative to the Freon fluids. Other types of working fluids, as
well as waxes and metal hydrides, may be used in the thermal
actuator 1, depending on the operational criteria of the same,
including, for example, energization and recycling, normal ambient
temperatures, and the like.
The guide cap 3 is secured to the main body 2 by a folded flange 4a
and the internal surface of the guide cap provides an exterior
supportive function for the diaphragm cylindrical leg 22, which
increases and decreases in length as the diaphragm rolls along its
annular fold 23. A piston 24 inserted in the diaphragm cap portion
19 provides a supportive function for the cap portion and transmits
the mechanical output of the thermal actuator 1 via the piston rod
5 as the cap portion projection into the chamber 14 is varied. The
piston 24 and piston rod 5 may be integral or separate connected
pieces and may be formed of metal, plastic, or other relatively
strong rigid material. Preferably the opening 6 in the guide cap 3
is relatively smooth to avoid scarring the piston rod as the latter
moves in an out. Moreover, the piston 24, which is of generally
cylindrical profile with a solid end engaged with the diaphragm cap
portion, has an annular slot 25 that receives a portion of a light
force return spring 26 that also bears against the front end wall 7
of the guide cap 3 proximate the opening 6. The return spring
normally urges the piston 24 and diaphragm 10 to their position
shown in FIG. 1 when the actuator 1 is de-energized. Obviously by
using a relatively strong or heavy return spring 26, the actuator
would be double acting to provide output forces in both directions
as the piston rod 5 moves out and in upon energization and
de-energization of the actuator.
To operate or to energize the thermal actuator 1, electric power is
supplied to the heater 16, which preferably rapidly heats and also
rapidly effects vaporization of at least part of the working liquid
15 to increase the total fluid pressure within the fluid chamber
14. The increased fluid pressure then overcomes the force of the
return spring 26 and tends to push the projection of the diaphragm
cap portion 19 and piston 24 from its in-stroked position shown in
FIG. 1 toward its maximum outstroked position with the piston
travel being limited by abutment with the front end wall of the
guide cap 3, as shown in FIG. 2, while the piston rod 5 then may
perform work on an external device, not shown. When the actuator 1
is in its de-energized condition, the fluid chamber 14 is
preferably filled with the working liquid 15 for optimum operation
regardless of the orientation of the thermal actuator, and thus
assuring that the heater 16 will be fully submerged and to an
extent cooled by the liquid to prevent burning out. Of course as
the piston and diaphragm projection is moved to the out-stroked
position, as shown in FIG. 2, a portion of the working liquid will
have been vaporized, as is indicated, for example, at 15a. It will
also be clear that as the diaphragm 10 rolls along its annular fold
23, the cap portion 19 and the further cylindrical leg portion 22
are substantially fully supported, respectively, by the piston 24
and the guide cap 3, thus increasing the longevity of the
diaphragm.
In the event that undesirable excessive pressure builds up in the
fluid chamber 14, after the piston 24 and diaphragm cap portion 19
have moved fully to the out-stroked position, the diaphragm may
stretch somewhat along its annular fold 23 until the annular fold
engages the step 9 in the guide cap 3, the cooperable piston
cylindrical body and the reduced diameter of the guide cap
preventing further diaphragm extension beyond that point.
Thereafter, a continued increase in the fluid pressure will cause a
portion of the diaphragm to protrude into and through the pressure
relief opening 8; and as the protrusion continues to expand, it
will ultimately rupture or blow-out in the direction of the arrow
27 to release fluid from the fluid chamber 14 and thus relieve the
pressure therein. The pressure level at which such rupturing occurs
may be controlled by varying the dimensions of the pressure relief
opening 8 as well as the materials and other designed
characteristics of the diaphragm 10. Moreover, the pressure relief
operation may occur in a somewhat modified manner, whereby a
portion of the diaphragm along its annular fold 23 ruptures before
stretching to engagement with the guide cap step, and in such event
the excessive fluid pressure would be relieved through the pressure
relief opening 8 via the annular space 28 remaining between the
diaphragm annular fold 23 and the guide cap step.
A thermal actuator in accordnace with the described invention was
successfully built and tested. The main body of such actuator had a
cross-sectional diameter of approximately 1/2 inch, and the
extensible diaphragm member therein was an unreinforced diaphragm
manufactured by the Geneva Rubber Company. The actuator was
energized for normal operation and developed approximately 100 psi
pressure in the fluid chamber with a corresponding output force at
the piston rod 5 on the order of approximately 15 pounds over a
stroke distance of approximately 1/2 inch. The diameter of the
pressure relief opening 8 was on the order of 3/32 of a inch, and
in several actuators tested for blow-out operation, for exapmle, by
maintaining the heater energized well after the piston reached
abutment with the front guide cap wall, blow-out and pressure
relief occurred at an average pressure in the fluid chamber 14 on
the order of 260 psi. This last pressure is well below that at
which the parts of the actuator would become disassociated.
Turning now more particularly to FIGS. 3 and 3A, there is
illustrated a thermal actuator 30 that is substantially identical
to the thermal actuator 1 described above with the exception of the
configuration of the guide cap 31 and piston 32. In the actuator 30
the guide cap 31 is substantially completely cylindrical and the
size of the opening 6 through which the piston rod 5 extends
provides suitable clearance with the latter for blow-out and
pressure relief through such clearance. A skirt 33 added to the
piston 32 has an outer circumference approximately equal to the
inner circumference of the guide cap 31 in order to cooperate with
the latter to assure linear motion and guidance of the piston and
piston rod during operation of the actuator. A slot 34 in the
piston skirt 33 provides for pressure relief in the fluid chamber
in a manner to be described below. In nomral operation of the
thermal actuator 30 the slot 34 has substantially no affect and the
actuator may be energized and de-energized in the above-described
manner; however, during such operation the piston skirt cooperates
with guide casing 31 and the piston rod 5 cooperates with walls
defining the guide cap opening 6 to maintain linear movement of the
piston and piston rod and accurate support of the diaphragm cap
portion 19.
An excessive pressure build up in the fluid chamber 14 of the
thermal actuator 30 will cause the diaphragm 10 to stretch at its
annular fold 23 in the manner described above, and ultimately and
diaphragm will rupture or blow-out at the annular fold and
preferably at the slot 34 to release fluid through the slot 34 and
the clearance at the opening 6. The blow-out pressure may be
determined, for example, by the dimensions of the slot 34 and/or by
the diaphragm composition. Upon blow-out the reduced pressure in
the fluid chamber 14 may permit the piston to move slightly inward
from the front end wall of the guide cap 3 or the spring 26 may
preclude the piston from abutting such end wall in order that the
flat annular wall 35 does not seal with the latter and preclude
pressure relief. Alternatively, the slot 34 may be cut to the
return spring slot 25 to ensure fluid communication with the
clearance at the opening 6 or an additional blow-out hole, not
shown, may be formed in the front end wall 7 of the guide cap
31.
Referring now more particularly to FIGS. 4 and 4A, a thermal
actuator 40 is similar to the above-described thermal actuator 1
with the exception of the formation of the guide cap 41, and normal
operation of the thermal actuator 40 is similar to that described
above with reference to the thermal actuator 1. The guide cap 41 is
annularly stepped at 42, and that annular step is interrupted by an
embossment 43, the shape of which is most clearly illustrated in
FIG. 4A. When the thermal actuator 40 becomes overloaded, the
diaphragm 10 may stretch at its annular fold until substantially
all of the diaphragm becomes supported at the annular step 42,
except for that portion of the diaphragm which is permitted to
stretch further into the further void defined by the embossment 43,
and it is this latter portion of the diaphragm that will tend to
burst to relieve pressure in the fluid chamber 14. The excess fluid
may be released either through a clearance provided at the opening
6, as described above with reference to the thermal actuator 30 in
FIG. 3, or an additional fluid release opening may be supplied in
the embossment 43.
In FIG. 5 the thermal actuator generally indicated at 50 is similar
to the above-described thermal actuator 1 with the exception of the
formation of the guide cap 51 and the piston 52. The guide cap 51
has two substantially cylindrical portions 53, 54 which are
connected at a solid annular step 55. Moreover, the piston 52 has a
longitudinal slot 56 formed in its otherwise substantially solid
outer periphery. The slot 56 may have parallel or angular sides as
can be seen more clearly in FIGS. 5A and 5B, respectively, wherein
the parallel sides 57a, 58a of a slot 56a in piston 52a are shown
in the former and the angular or tapered sides of the slot 56b in a
piston 52b are indicated at 57b, 58b in the latter. The pistons
52a, 52b, respectively illustrated in FIGS. 5A and 5B correspond to
the piston 52 shown in the thermal actuator 50 of FIG. 5, the only
distinction being the particular shape of the respective slots 56a,
56b, and either piston may be used in the thermal actuator 50,
depending on the desired blow-out pressure and/or characteristics
of the thermal actuator 50.
Operation of the thermal actuator 50 under normal conditions is
substantially the same as described above with reference to the
thermal actuator 1 of FIG. 1. However, in the event of excessive
pressure build up in the fluid chamber 14, the portion of the
diaphragm leg 21 located above the piston slot 56 will deform into
the latter and ultimately will perforate to release fluid to the
clearance provided at the opening 6 in the front end wall 7 of the
guide cap 53 via the cylindrical return spring slot 25 in the
piston 52.
It should now be understood that the present invention provides for
a controlled blow-out or pressure relief in a fluid actuator
device, regardless of whether such device is energized by
application of an external fluid, application of heat or cold,
application of electrical power, or the like. By incorporating the
present invention in a fluid actuator, the several actuator parts
desirably fully maintain their integrity in the course of normal
operation; however, in the event of abnormal conditions, regardless
of the cause, that effect an undesirable excessive pressure build
up in the actuator, controlled pressure relief is provided by self
or cooperative destruction of one or more of the actuator parts
while preferably maintaining maximum external integrity of the
actuator.
* * * * *